The present invention relates to a portable radio apparatus and an antenna apparatus which are suitably used for a portable telephone.
Recently, the compact and lightweight design of portable telephones has been required in order to enhance portability, and in accordance with this requirement a small antenna has been widely used this whip type antenna is retracted in the main body when it is carried and drawn out of the main body during a telephone call.
Accordingly, damage of the antenna can be prevented when it is carried, also deterioration of radiation characteristics such as reduction in antenna gain due to the effect of a human body, particularly the head can be avoided by increasing the antenna length (effective height) during a telephone call. This will enhance, so that the telephone quality.
On the other hand, due to a further compact design of portable telephones, the distance between a transmitter (microphone) and a telephone receiver (speaker) cannot be set to be equal to the distance between the mouth and the ear of a human. Therefore, there has been proposed a portable telephone in which a microphone is separated from the main body of the portable telephone and accommodated in a rotatable portion (microphone arm) which can be retracted in and drawn out the main body, the microphone arm is retracted when it is (carried while it is drawn out when it is used for a telephone call, so that the microphone is located near to the mouth.
Further, there has been known a compact portable telephone in which an antenna is embedded in the microphone arm to enable an antenna and a microphone to be drawn out with one stroke under a telephone call as shown in FIG. 1.
That is, as shown in FIG. 1, in a conventional compact portable telephone 10, on the front surface of a housing 11 of the telephone body are usually formed an opening 12 for a telephone receiver (speaker), and operation keys 13 such as a dial key, etc. Further, a liquid crystal display element 14 is disposed between the opening 12 and the operation keys 13.
In the housing 11 is accommodated a circuit board on which an RF transmission/reception circuit, an antenna matching circuit, a voice processing circuit, etc., not shown, are mounted. The RF transmission/reception circuit and the antenna matching circuit are disposed in a shield case.
A protection plate 15 having an "L"-shaped section is provided integrally with the housing 11 at the further right side of the right-side wall 11r of the housing 11 which is formed of suitable synthetic resin material. A small-diameter rotational shaft 22a of a rotational end portion 22 of the microphone arm 21 which is formed of suitable synthetic resin material is freely rotatably engaged with the lower portion of the right-side wall 11r of the housing 11.
The microphone 23 which is embedded in a free end portion 21f of the microphone 21 is connected through a voice signal line 24 to the voice processing circuit on the circuit board, and the base portion 25b of a rod antenna 25 which is embedded in the microphone arm 21 and is formed by designing a conductor of predetermined length in a linear form is connected through a feeder spring 26 to an antenna matching circuit on the circuit board as described above.
When the portable telephone 10 is carried, the microphone arm 21 is retracted while sandwiched between the right-side wall 11r of the housing 11 and the protection plate 15 as indicated by a solid line of FIG. 1.
When the portable telephone 10 is under the telephone call, as shown by a chain line of FIG. 1, the microphone arm 21 is rotated in a counterclockwise direction from the retracted state as described above, ani drawn out so that the microphone 23 and the housing 11 are intersected to each other at a suitable obtuse angle and the microphone 23 and (the opening for) the speaker 12 are kept to be away from each other at a predetermined distance. In addition, deterioration of radiation characteristics such as reduction in antenna gain, etc. due to the effect of the human head is avoided.
In such a state that the microphone arm 21 is drawn out as described above, the microphone 23 is located at a lower position than the bottom surface 11b of the housing 11 in FIG. 1.
Further, by disposing a rod antenna 25 in the microphone arm 21, the portable telephone 10 as described above needs no antenna accommodating space in the housing 11, and this is effective to miniaturize the portable telephone 10. Still further, if the rod antenna 25 of super elastic member such as Ni--Ti alloy, for example, this is effective to reinforce the microphone arm 21.
In the conventional compact portable telephone 10 as described above, however, the free end portion 21f is not located at a higher position than the upper surface lit of the housing 11 in the figure in the state where the microphone arm 21 is retracted. Accordingly, the rod antenna 25 is located so as to be proximate to the ground conductor of the circuit board and the shield case through the right-side wall 11r of the housing 11 over the entire length thereof. Therefore, the input impedance of the rod antenna 25 is greatly increased, and thus the rod antenna 25 does not establish the match with a feeding system which is represented by a feeder spring 26, so that the matching loss therebetween is increased and no excellent antenna characteristic can be obtained.